The present invention relates to a vacuum actuated system, such as an exhaust gas recirculation (EGR) control system or a spark timing control system.
It is known to operate a vacuum servo means for an EGR control valve on a single vacuum at a certain vacuum port above the idle speed position of the throttle valve. Operation of the vacuum servo means for the EGR control valve on the single vacuum involves the following problem. If the contour of a valve member of the EGR control valve and the spring constant of a valve spring of the EGR control valve are designed so as to optimize EGR flow rate for operation at acceleration, the EGR flow rate becomes too high during operation in the vicinity of road load (R/L), while if the contour of the valve member and the spring constant of the valve spring are designed so as to optimize EGR flow rate for operation in the vicinity of road load (R/L), the EGR flow rate becomes too little during operation at acceleration. Thus with the known EGR control system it is difficult to precisely control the engine.